With developments of electronic circuits, digital processing bits increase in number and digital processing speed becomes faster and faster. Consequently, the number of pins of corresponding sockets must also increase. Thus, sockets having many pins have become more frequent and more important.
A socket is mounted on a circuit board through surface mount technology (SMT), which often involves solder balls being disposed at a solder jointjoint of each terminal of the socket through pre-soldering or planting solder balls. However, this technique often results in open solder joints.
FIG. 1 shows a top plan view of a socket. FIG. 2 is a schematic view showing solder balls being planted at terminals of the socket of FIG. 1. FIG. 3 is a bottom plan view of a part of FIG. 2. FIG. 4 is a schematic view showing solder balls being pre-soldered to terminals of the socket of FIG. 1.
Referring to FIGS. 1˜4, a conventional socket A (with pre-soldered solder balls or planted solder balls) includes a dielectric housing 1, a plurality of terminals 2 and a plurality of solder balls 3.
As shown in FIGS. 2 and 3, as to the socket with planted solder balls, the plurality of terminal passages 11 is perpendicularly defined in the dielectric housing 1. A receiving cavity 12 is defined at the bottom of each terminal passage 11 for receiving the solder ball 3. The terminals 2 are respectively received in the terminal passages 11. Each terminal 2 has a contact portion 21 at the upper end thereof and a solder joint 22 at the lower end thereof. The contact portion 21 is resiliently and electrically connected with a corresponding contact of an electronic module (not shown). The solder joint 22 downwardly extends and locates at a side wall of the receiving cavity 12. The plurality of solder balls 3 is respectively buried between the receiving cavities 12 and the solder joints 22. Each solder joint 22 and each solder ball 3 are secured in the receiving cavity through height and pressing force of a plurality of pressing walls 13 formed by the four side walls of each cavity 12 and an abutment of the bottom wall 14 of each receiving cavity 12, for soldering to a circuit board 4.
To prevent it from falling out, the planted solder ball 3 must be pressed to fix between the receiving cavity and the solder joint 22 of the terminal 2. That is, the solder ball is buried and pressed between the solder joint 22 and the four pressing walls 131, 132, 133, 134 of the receiving cavity 12.
Referring to FIG. 4, as to a socket with pre-soldered solder balls, the basic structure is similar to that of the socket with planted solder balls, except that the bottom end of the solder joint 22 of each terminal 2 is pre-soldered with a solder ball 3 for fixing the solder ball 3 at the solder joint 22 of the terminal 2.
When the solder ball 3 is disposed at the conventional solder joint 22 of the terminal 2 through planting or pre-soldering, the solder ball 3 is fixed at the solder joint 22. That is the position of the solder ball 3 cannot be adjusted up and down, and thus all the solder balls are kept at the same height such that the solder balls can fully make contact with a perfectly flat circuit board 4.
However, the surface of the circuit board 4 is not often precisely flat; sometimes the surface of the circuit board is slightly warped or deformed due to temperature or load. Consequently, the warped or deformed surface of the circuit board 4 cannot fully contact the solder balls 3. For example, when a gap is formed between a concave surface 41 of the circuit board 4 and each solder ball 3a, the solder balls 3a cannot contact the surface of the circuit board 4 during soldering, which results in open solder joints.
Therefore, it is desired to ensure that each solder ball fully contacts the circuit board.